Cooled airfoil and method of making it

ABSTRACT

A TRANSPIRATION-COOLED TURBINE VANE OR THE LIKE HAS NUMEROUS PORES FOR EMISSION OF AIR FROM THE VANE FOR TRANSPIRATION COOLING. THESE PORES ARE PROCUCED BY PHOTOETCHING PITS FROM THE OUTER AND INNER FACES OF THE OUTER METAL LAYER OF THE VANE WALL, THE PITS BEING OFFSET SO THAT THEIR INTERSECTION HAS AN AXIS AT AN ACUTE ANGLE TO THE SURFACE OF THE VANE, WITH THE RESULT THAT THE AIR EMITTED FLOWS GENERALLY WITH THE DIRECTION OF FLOW PAST THE VANE RATHER THAN TRANSVERSE TO THE DIRECTION OF FLOW.

Oct. 24, 1972 T. H. MAYEDA 3,700,418

OOLED AIRFOIL AND METHOD OF MAKING IT Filed Nov. 24, 1969 ,IIJVII Q f A" INVENTOR.

fiamsHMag zzda 24m 77m AT TORNEY United States Patent 3,700,418 COOLED AIRFOIL AND METHOD OF MAKING IT Thomas H. Mayeda, Speedway, 1nd,, assignor to General Motors Corporation, Detroit, Mich. Filed Nov. 24, 1969, Ser. No. 879,094 Int. Cl. B26f l /00,- C23b 1/02; F03b 3/00 U.S. Cl. 29180 SS Claims ABSTRACT OF THE DISCLOSURE A transpiration-cooled turbine vane or the like has numerous pores for emission of air from the vane for transpiration cooling. These pores are produced by photoetching pits from the outer and inner faces of the outer metal layer of the vane wall, the pits being offset so that their intersection has an axis at an acute angle to the surface of the vane, with the result that the air emitted flows generally with the direction of flow past the vane rather than transverse to the direction of flow.

The invention herein described was made in the course of work under a contract or subcontract thereunder with the Department of Defense.

DESCRIPTION My invention relates to improvements in turbine vanes and blades and other such devices which are protected from high temperature gas by discharge of a cooling gas through numerous pores distributed over the surface of the vane or the like. This mode of cooling is referred to as transpiration cooling.

My invention is particularly adapted to transpiration cooled vanes and blades of the general sort described in prior patent applications, of common ownership with this application, as follows: Bratkovich and Meginnis, Ser. No. 526,207 for LaminatedPorous Metal, filed Feb. 9, 1966; Pat. No. 3,584,972, Emmerson, Ser. No. 691,834 for Turbine Cooling, filed Dec. 19, 1967; Helms, Ser. No. 707,556 for Turbine Blade, filed Feb. 23, 1968; and Meginnis, Ser. No. 742,900 for Turbine Blade, filed July 5, 1968, Pat. No. 3,619,082.

These applications describe turbine vanes or blades having laminated walls, the outermost layer of which has pores whtich are machined in the surface of the layer by a process such as photoetching to provide numerous outlets for cooling air or other gas from the interior of the vanes or blades. Vanes, blades, or other structures to be protected from hot gas by transpiration cooling will be referred to hereafter in this specification as vanes for conciseness.

It has been found that the discharge of the coolingair from the surface of the vane has some adverse effect upon the efficiency of the turbine or other aerodynamic machine. This appears to be due to some interference between the cooling air coming out substantially perpendicularly from the vane surface and the motive fluid or other gas flowing substantially tangentially to the surface.

It has occurred to me that, by a modification of the structure of the pores from which the cooling air is discharged from the outer surface of the blade, this interference may be substantially reduced and the efiiciency of the turbomachinery correspondingly enhanced.

In the preferred embodiment of my invention, this is accomplished by angling the pores in the vane facing or outer layer by photoetching pits in from both the outer and inner surfaces of the layer, with the two sets of pits offset so that the intersection between them has an axis substantially inclined to the normal to the surface and so 3,700,418 Patented Oct. 24, 1972 that the gas discharged from the pore is directed largely downstream with respect to the motive fluid flow past the vane.

The principal objects of my invention are to improve the efficiency and temperature tolerance of high temperature turbomachinery; to improve the efliciency of transpiration cooled vanes, blades, and other elements of engines; and to provide a simple and elfective means for discharging transpiration cooling air from a vane in a direction largely conforming to the flow past the vane rather than directly transverse to such flow.

The nature of my invention and its advantages will be clear to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings thereof.

FIG. 1 is an axonometric view of a transpiration cooled turbine vane.

FIG. 2 is a transverse sectional view of a prior art vane, taken on the plane indicated by the line 22 in FIG. 1, illustrating the discharge of cooling air from the outer surface of the prior art vane.

FIG. 3 is a view similar to FIG. 2 showing the discharge of transpiration cooling air from a vane in accordance with my invention.

FIG. 4 is a greatly enlarged fragment of FIG. 3 illustrating more clearly the nature of the pore formation in the vane wall.

Referring first to FIG. 1, this illustrates a hollow tubular member 6 which may be a turbine vane airfoil or the airfoil portion of a turbine blade or might represent some other structure in a high temperature machine such as a turbine. The airfoil 6 is a hollow tubular structure having a formed outer wall 7 perforated by numerous small closely spaced pores 8. As previously stated, this structure as so far described may be similar to those described in the abovementioned patent applications.

FIG. 2 is a partial illustration of structure of such a vane in accordance with the prior applications in which the wall 7, which is the outermost layer of the blade wall, is broken by numerous more or less evenly spaced small transpiration air discharge pores 8. FIG. 2 also illustrates an inner layer 10 bonded to the layer 8 and spaced from it by numerous bosses 11, the layer 10 having holes 12 through it through which the cooling air is supplied from the hollow interior 14 of the vane to the pores 8. As shown in the prior applications, the laminated structure may have various forms and, so far as the present invention is concerned, the blade wall is not necessarily laminated.

However, as a practical matter, to provide the small pores in the outer surface of the blade which normally are provided by photoetching, it is preferred to have the outer layer approximately .010 inch thick. With this sort of material it is in most cases highly desirable to provide additional layers within the outermost layer. Be that as it may, my invention is not dependent upon the interior structure of the blade or vane but is directed particularly to improving the outermost layer which is in contact with the motive fluid or other gas flowing past the blade.

As indicated by the legend FLOW and the arrows at the left of FIGS. 2 and 3, the flow of motive fluid such as hot combustion products, for example, is from the leading edge 15 of the vane 6 past both faces of the vane to the trailing edge 16. With the structure illustrated in 'FIG. 2, the outflow of transpiration cooling air is generally perpendicular to the surface of the vane as indicated by the numerous small arrows 18. As previously stated, the vane according to by invention has the structure of the holes in the outer layer 22 such that the air flow from the transpiration cooling pore 23 is at a substantial angle to the normal to the blade surface and is, in general, in a downstream direction consistent with the flow of motive fluid past the blade, as indicated by the small arrows 24. It will be understood that one or more or more additional layers of metal may be provided inside the illustrated layer 22, as described in prior applications, but that is not material to the present invention.

As shown clearly in the greatly enlarged view of FIG. 4, the outer sheet, wall, or layer 22 which, for example, may be .010 inch thick, has the pores 23 each defined by a pit 26 extending into the inner surface 27 of the sheet 22 and a pit 28 extending into the outer surface 30 of the sheet. As illustrated, these pits are of a character which is produced by chemical machining, specifically by photoetching, which is the preferred way to form the pits required for transpiration cooling, particularly in refractory metals of the sort used in high temperature machines.

Referring again to FIG. 4, the axis or center of the pore 23 made up by pits 26 and 28 may be considered to be on the line 31. The machining of the pores is accomplished by coating the surface with a resist except for small spots indicated by the lines 32, 33, 34, and 36 indicating the boundaries of the clear area on the two surfaces of the sheet. When the sheet is immersed in the etching solution, the metal is eaten away beyond the boundaries of the clear spot generally as shown, to provide two roughly hemispherical or hemispheroidal pits which are allowed to grow until they intersect to provide the air hole where the pits merge through which the cooling air flows as indicated by the arrow 38 in FIG. 4

In the example illustrated, the line 33 and 34 are each offset about 0.003 of an inch from the line 31, this being for a sheet 0.010 inch thick. The preferred maximum diameter of the intersection between the two pits is 0.010 to 0.012 inch. By varying the etching process, some control of the magnitude of these air holes may be effected.

Experiments have shown that, in a structure according to the invention, the direction of air flow as indicated by arrows 24 or 38 can be as low as 30 with respect to the surface of the sheet 22. The result in operation of an engine is a substantial reduction in interference between the cooling air fiow and the motive fluid and less tendency for the cooling air flow to separate from the surface of the vane. As a result, the cooling is improved and the aerodynamic efficiency enhanced.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, as many modifications may be made by the exercise of skill in the art.

I claim:

1. A method of producing a metal sheet having pores distributed over the sheet adapted to flow a gas through the sheet at an actuate angle to the surface of the sheet comprising machining a rounded pit in one surface of the sheet at the location of each pore and machining a rounded pit in the other surface of the sheet offset from but tangentially intersecting each pit in the said one surface so as to provide the pore opening between the intersecting pits directed at an acute angle to the surface of the sheet.

2. A method as recited in claim 1 in which the pits are machined by chemical etching.

3. A method of producing a transpiration-cooled airfoil comprising forming the exterior of the airfoil from a sheet produced by the method defined in claim 1.

4. A method of producing a transpiration-cooled airfoil comprising producing a sheet by the process recited in claim 1 and thereafter forming the sheet to an airfoil contour.

5' A hollow airfoil having a porous exterior sheet for transpiration cooling of the airfoil by a cooling gas discharged from the interior of the sheet through pores in the sheet to the exterior thereof characterized by array of pores extending through the said sheet; each pore being defined by two tangentially intersecting pits extending into the exterior and interior faces of the sheet, respectively, the pits extending into the interior face being upstream, with reference to the direction to flow past the airfoil, with respect to the pit extending into the exterior face, the opening defined by the intersection between the said pits having an axis directed at an acute angle to the face of the sheet.

6. An airfoil as defined in claim 5 in which the pits are of a roughly hemispheroidal configuration.

7. A sheet having a porous exterior surface for transpiration cooling of the sheet by a cooling gas discharged from the rear surface of the sheet through pores in the sheet to the exterior thereof characterized by an array of pores extending through the said sheet configured to direct the gas at an acute angle to the surface of the sheet in a direction downstream relative to flow past the sheet in normal operation, each pore being defined by two tangentially intersecting pits extending inwardly substantially perpendicularly from opposite surfaces of the sheet, the pits having offset centerlines and intersecting at a surface making an acute angle to the surface of the sheet.

8. An airfoil having an exterior surface defined by a sheet as recited in claim 7.

9. A hollow airfoil having a porous exterior sheet for transpiration cooling of the airfoil by a cooling gas discharged from the interior of the sheet through pores in the sheet to the exterior thereof characterized by an array of pores extending through the said sheet configured to direct the gas at an acute angle to the surface of the sheet in a direction downstream relative to flow past the airfoil in normal operation, each pore being defined by two tangentially intersecting pits extending inwardly substantially perpendicularly from opposite surfaces of the sheet, the pits having offset centerlines and intersecting at a surface making an acute angle to the surface of the sheet.

10. A hollow airfoil as defined in claim 9 in which the exterior sheet is approximately one-hundredth inch thick.

References Cited UNITED STATES PATENTS 767,367 8/1904 Westinghouse 29-163.5 UX 1,295,291 2/1919 Fasting 209-397 UX 1,341,187 5/1920 McPheeters 210-498 X 1,900,960 3/1933 Takeda 153-3 3,457,619 7/1969 Kydd 29-1635 X 3,546,075 12/1970 Sheetz et al. 29-180 SS X FOREIGN PATENTS 20,615 12/1913 Denmark 210-498 ALLEN B. CURTIS, Primary Examiner US. Cl. X.R. 

